Manipulability is addressed experimentally in a different working paper. The participants weren't told the internals and the manipulations were mostly hypothetical, but honesty was the highest scoring strategy in what they considered.

In some sense, it's easy to manipulate BTS to give a particular answer. The only problem is you might end up owing the operator incredibly large sums of money. If payments to and from the mechanism aren't being made, BTS is worthless if people try to game it. I should have a post up shortly about a better mechanism.